I'm sorry your dog got killed on the highway and I'm sure you and your wife are upset about it. Do you suppose the poor sucker that hit the dog felt anything? I can tell you first hand it's not a fun thing to kill a dog with your car and you don't have to be speeding. I killed my neighbors dog going 15mph right in front of his two young kids and wife. I felt terrible but there wasn't anything I could do when it ran right in front of the car. I locked up the brakes and skidded on the gravel, the right front wheel went over the dog crushing his shoulder. There was nothing that could be done for him except put him down.
The neighbor has an "invisible" fence but it fails often and it takes him a long time to fix it. The dogs figure out pretty quickly when it's not working and start playing chicken with me. I've requested many times that he fix it and warned him what would happen if he didn't. That said, I still felt terrible when it happened and cringe every time his new dog charges my car. To his credit, he spent the money to buy a tester and the fence is working now.
I'm not going to offer any advice, I give enough to my neighbor and don't feel good about it.
Kevin